1. Field of the Invention
The present invention relates to an engine stop control device having a function to control an engine rotation stop position (stop crank angle) when an engine stops.
2. Description of Related Art
In recent years, as described in Patent document 1 (JP-A-2005-315202), there has been a vehicle mounted with an engine automatic stop-start system (idle stop system) that performs control for increasing a target current value of an alternator to an initial value set at a large value beforehand and then decreasing the target current value when an engine is stopped automatically, aiming to control an engine rotation stop position (stop crank angle) into a crank angle range, which is suitable for start, during engine stop (idle stop) and to improve restarting performance.
An engine stop control device described in above Patent document 1 controls the engine rotation stop position into the target crank angle range by controlling a load of the alternator when automatically stopping the engine. However, practically, the control device merely sets the target current value of the alternator in accordance with present engine rotation speed with the use of a preset map when the engine rotation speed, which is sensed when a piston passes a compression top dead center (TDC), is in a range from 480 rpm to 540 rpm (refer to paragraph 69 of Patent document 1). Therefore, the control of the alternator load is rough and it is difficult to sufficiently compensate a variation in an engine rotation behavior during an engine stop process. Therefore, it is thought that the control device of Patent document 1 cannot reduce the variation in the engine rotation stop position sufficiently and cannot exert a sufficient effect to improve the restarting performance.
In order to solve the problem, the applicant of the present application filed patent applications of an invention for calculating a target engine rotation behavior (referred to as target trajectory, hereinafter) extending until engine rotation stops at a target stop position and for controlling an accessory load of an engine to conform an engine rotation behavior to the target trajectory as described in specifications of Japanese Patent Applications No. 2007-53598 and No. 2007-54775.
In the engine stop process, cylinder pressure changes with compression and expansion of cylinder air caused by rotation of the engine. The cylinder pressure at the engine rotation stop changes in accordance with a crank angle at the engine rotation stop and therefore compression torque (torque caused by cylinder pressure) acting on a crankshaft changes. Accordingly, the target trajectory suitable for stopping the engine rotation at the target stop position also changes. In the invention of the above applications, such the change in the target trajectory is not taken into account. Therefore, accuracy of the target trajectory worsens correspondingly.
In order to solve such the problem, the applicant of the present application filed an application of an invention for correcting the target trajectory in accordance with the target stop position in consideration of an influence of the compression as described in a specification of Japanese Patent Application No. 2007-325520. According to the invention, the target trajectory can be set accurately when there is no error. However, a characteristic of a friction or compression governing the engine rotation stop behavior changes due to oil temperature, oil degradation, aging change and the like. Therefore, in order to accurately set the target trajectory, it is necessary to learn the friction and the compression from a stop position error separately. However, it is difficult to learn the compression and the friction from the stop position error separately.